Following drilling operations, oil and gas producers are often faced with the problem of freeing deposits from the well hole site. Since many of the easily obtainable energy sources have already been harvested, a large number of the remaining sites are trapped within hard rock and sandstone substrates. Such wells are often abandoned because of an inability to perforate these down-hole geological formations. Improved means for enhancing penetration, therefore, would be expected to result in a significant economic gain in oil and gas production.
The art has previously resorted to shaped explosive charges for perforating the solid rock to reach these otherwise inaccessible reserves. These charges have been known to create fissures in the deposit substrates, whereby channels are generated between the oil and gas reservoirs and the well bore. In most of the commercially-available shaped charges, a metal tube containing a common explosive material, such as C6, is provided with an initiating charge containing, for example, a simple cylindrical pellet booster. A conically-shaped metal liner is inserted into the front of the tube and into the explosive material for aiding penetration into the hard rock formations upon detonation of the charge. Such liners typically employ a soft ductile, low density metal, such as copper or iron. The principles of shaped charge functioning are well known, and are described in G. Birkhoff et al., Journal of Applied Physics, Vol. 19, p. 563-82 (June, 1948), and M. Cook, The Science of High Explosives, Chapter 10, Reinhold Publishing Corp., New York (1958), which are hereby incorporated by reference.
The penetration of a shaped charge into a solid hard rock formation is known to be governed by the following calculation, hereinafter referred to as the "penetration formula". ##EQU1## Where P=penetration into a given target in units of distance
l=the length of the metal jet PA1 P.sub.i =the density of the jet metal in g/cc PA1 P.sub.m =the density of the material being penetrated in g/cc
From this equation, it is clear that by maximizing the ratio of the metal jet density, "P.sub.i ", to the target density, "P.sub.m ", a greater penetration, "P", into the formation can successfully be achieved. Additionally, greater ductility is also important, since it is directly related to the length, "l", of the jet. Finally, the factor "K" in the above equation relates to the explosion system considerations for a given charge, such as its explosive impetus, which provides yet another factor for optimizing perforator designs.
Accordingly, there is a need for a more effective charge design which permits higher perforation of hard rock geological deposits during oil and gas recovery operations. There is also a need for improved liner materials, and more effective charge initiation schemes.